Branch: refs/heads/blead
Home: https://github.com/Perl/perl5
Commit: 9a224d076a17344e9e851460223544deb2a30532
https://github.com/Perl/perl5/commit/9a224d076a17344e9e851460223544deb2a30532
Author: David Mitchell <da...@iabyn.com>
Date: 2024-06-19 (Wed, 19 Jun 2024)
Changed paths:
M ext/B/t/optree_varinit.t
M peep.c
M pp_hot.c
M t/perf/opcount.t
Log Message:
-----------
OP_PADSV_STORE: only in void context
(The original commit, v5.39.6-108-gc90e7ed39e, was reverted by
v5.39.8-35-gdc524b6cbd, and is now being re-applied. Originally it broke
some CPAN distributions and as it was near code-freeze time and was only
an optimisation, it seemed better to leave it for later. Since we're now
early in the cycle of 5.41.x, there's more time to fix up any fallout.)
----
For the optimisation which converts $lex = expr into an OP_PADSV_STORE
op, only optimise if the scalar assign is in VOID context.
This allows us to stop pp_padsv_store() from uselessly pushing the
result onto the stack, only to be immediately popped again by the
following nextstate or unstack op. This becomes more important on
PERL_RC_STACK builds, as each push or pop involves manipulating the SV's
reference count.
I'm working on the assumption that scalar/list/unknown cxt lexical
assigns are rare enough that not optimising them is less of a loss than
optimising the void case. So:
$lex = ....; # void: now even faster
$other = $lex = ...; # scalar: now slow again
foo($lex = ..., ....); # list: now slow again
sub {
....
$lex = ...; # unknown: now slow again
}
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